This invention regards a device for reducing the proportion of volatile organic compounds VOC that separates out from oil, especially during transport in large tanks, such as is common e.g. during sea transport.
Crude oil normally contains fractions of light and heavy gases that, due to their volatility, cannot be transported with the liquid fraction of the crude oil. In terms of the technical aspects of the transport, it would be favourable if the crude oil were separated into a gas fraction, a liquid gas fraction and a liquid fraction. However, separating and transporting petroleum products from a production field in three fractions involves considerable extra costs, and as such the crude oil is normally separated into a gas fraction and a liquid fraction. The liquid gas phase is therefore divided into a lighter fraction to be transported with the gas fraction and a heavy fraction to be transported with the liquid fraction.
When transporting a liquid petroleum fraction containing heavy gases such as propane and butane at a moderate gauge pressure of the order of 1.05 to 1.07 bar, gases will continuously evaporate from the liquid fraction. To avoid a pressure increase in the transport tanks, the evaporating gases, i.e. the volatile organic compounds, must be drawn off from the tanks and sent to combustion or a reinjection plant.
NO 19996471 concerns a downcomer provided with a venturi, the venturi being designed to condense already separated gases from a cargo hold. By using a venturi to increase the fluid velocity and thereby the underpressure, unnecessary evaporation of VOC is anticipated due to the relatively low pressure.